The actions of many extracellular signals (for example, neurotransmitters, hormones, odorants, light) are mediated by receptors with seven transmembrane domains (G protein coupled receptors) and heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins). See H. Dohlman, M. Caron, and R. Lefkowitz, Biochemistry 26, 2657 (1987); L. Stryer and H. Bourne, Ann. Rev. Cell Biol. 2, 391 (1986). Such G protein-mediated signaling systems have been identified in organisms as divergent as yeast and man. See H. Dohlman et al., supra; L. Stryer and H. Bourne, supra; K. Blumer and J. Thorner, Annu.Rev. Physiol. (in press). The .beta.2-adrenergic receptor (.beta.AR) is the prototype of the seven-transmembrane-segment class of ligand binding receptors in mammalian cells. In response to epinephrine or norepinephrine, .beta.AR activates a G protein, G.sub.s, which in turn stimulates adenylate cyclase and cyclic adenosine monophosphate production in the cell. See H. Dohlman et al., supra; L. Stryer and H. Bourne, supra. G protein-coupled pheromone receptors in yeast control a developmental program that culminates in mating (fusion) of a and .alpha. haploid cell types to form the a/.alpha. diploid. See K. Blumer and J. Thorner, supra; I. Herskowitz, Microbiol. Rev. 52,536 (1988).
The present invention is based on our continued research into the expression of heterologous G protein coupled receptors in yeast.